A composite fabric comprising an expanded porous polytetrafluoroethylene (ePTFE) film and a cloth laminated to each other has been put to practical use as, for example, a clothing material excellent in moisture permeability and windbreak performance in the field of outdoor products and the like. Further, a composite fabric comprising a composite film having a waterproof property improved by applying a resin with moisture permeability to an ePTFE film and a cloth laminated to each other has also been put to practical use as, for example, a clothing material excellent in moisture permeability and waterproof property in the field of outdoor products and the like. A composite fabric comprising an ePTFE film alone is characterized by being excellent in moisture permeability and has been used as a material suitable for windbreakers or heavy winter clothes although the waterproof property of the composite fabric comprising an ePTFE film alone is inferior to that of a composite fabric comprising the composite film. In such composite fabrics, in order to increase a stretch property, a composite fabric comprising a composite film and a stretch cloth laminated to each other has also been known (Patent documents 1 and 2, etc.).
For example, in Patent document 1, a composite film comprising an expanded PTFE (i.e., sintered ePTFE) film and a hydrophilic elastomer layer provided by the technique described in U.S. Pat. No. 3,953,566, or a composite textile comprising this composite film and a fibrous outer layer (cloth) is stretched and released, whereby the stretch property and recovery property of this composite film or composite textile are increased. In this Patent document 1, the composite film or composite textile is stretched in one direction until a grip-to-grip distance of 9 inches becomes 18 inches (i.e., to about twice its original length), and at this time, necking occurs such that the sample width is decreased to about ⅜ to ½. When the present inventor made an additional test for this Patent document 1, the stretch property was not sufficient. Patent document 2 also describes that sintered PTFE as used in Patent document 1 “is poor in ductility because fibrils are fused to one another and interfibrillar slip does not occur” and points out that “the stretch property of the counterpart of the laminate is inhibited by the above-mentioned sintered PTFE and the stretch property of the laminate on the whole is hardly obtained”.
Accordingly, Patent document 2 has proposed that PTFE is used without being sintered (unsintered as such). Patent document 2 describes that when a stretch resin is impregnated into an unsintered ePTFE film and retained therein, favorable restoring property and stretch property can be achieved. However, the unsintered ePTFE film to be used in this Patent document 2 has a low cohesive strength in a thickness direction, therefore, a delamination phenomenon is likely to occur. In order to avoid the occurrence of this delamination phenomenon, it has been proposed that a stretch resin is applied to one surface or both surfaces. However, when such a stretch resin is applied to one surface, a cohesive strength of a surface without application of the stretch resin is apparently lacking. Further, even when the stretch resin is applied to both surfaces, if pores remain in the inside of the ePTFE film, the cohesive strength at the region is lacking. In order to completely prevent the occurrence of the delamination phenomenon, it is necessary to completely impregnate the stretch resin into the inside of the ePTFE film, inevitably resulting in increasing the thickness of the resin layer and decreasing the moisture permeability.
Further, because the methods described in Patent documents 1 and 2 utilize the stretch property of a resin to be applied to ePTFE, the methods cannot be applied to a composite fabric comprising an ePTFE film alone.
As described above, it is difficult to achieve both stretch property and strength (cohesive strength) in the prior art. Accordingly, in Patent documents 3 to 5, a method of laminating an ePTFE composite film to a cloth is improved instead of improving the physical property of an ePTFE composite film. That is, in these Patent documents 3 to 5, a stretch cloth is laminated to an ePTFE composite film in a stretched state, and thereafter, the stretch cloth is shrunk. FIG. 1 is a schematic cross-sectional diagram of such a laminate. As shown in FIG. 1, in examples of Patent documents 3 to 5, a pleated structure in which an ePTFE composite film 1a is corrugated along the stretching and shrinking direction of a cloth 2 is adopted. By adopting this pleated structure, the ePTFE composite film 1a follows the stretching of the cloth while eliminating the pleats when the cloth is stretched, therefore, a stretching stress does not act on the ePTFE composite film 1a, and even if sintered ePTFE is used (even if a strength is secured), the stretch property is not sacrificed. When such a pleated structure is adopted, however, the ePTFE composite film 1a has a corrugated form, therefore, the aesthetic appearance of a laminate 3 is deteriorated. In addition, the laminate 3 is likely to be rubbed against other members at tops 10 of the corrugated pattern, and the laminate 3 is liable to be damaged. Further, a used amount of the ePTFE composite film per unit area of the laminate is increased, and the production cost is increased.
The present invention has been made in view of the circumstances as described above and has its object to establish a technique capable of increasing a strength and a stretch property of an ePTFE film without corrugating the film.    Patent document 1: JP-A-S59 (1984)-187845    Patent document 2: JP-A-S61 (1986)-137739    Patent document 3: JP-A-H03 (1991)-90352    Patent document 4: JP-A-S60 (1985)-139444    Patent document 5: JP-T-1409 (1997)-500844